Why is Kaiping called three steps?

Changsha, Dihai and Xinchang, three commercial ports with a long history, are all built along the Tanjiang River. Kaiping is called Sanbu because from the early Ming Dynasty to the Guangxu period of Qing Dynasty, Changsha Port (1368- 1378) was built across the Tanjiang River, and the three ports were divided into seaports (185 1) and Xinchang Port (188/).